1. Technical Field
The present disclosure relates generally to radio frequency (RF) signal circuitry, and more particularly, to on-die harmonics filtering for RF power amplifiers.
2. Related Art
Wireless communications systems find application in numerous contexts involving data transfer over long and short distances alike, and there exists a wide range of modalities suited to meet the particular needs of each. Chief amongst these systems with respect to popularity and deployment is the mobile or cellular phone, and it has been estimated that there are over 4.6 billion subscriptions worldwide.
Generally, wireless communications involve a radio frequency (RF) carrier signal that is variously modulated to represent data, and the modulation, transmission, receipt, and demodulation of the signal conform to a set of standards for coordination of the same. Many different mobile communication technologies or air interfaces exist, including GSM (Global System for Mobile Communications), EDGE (Enhanced Data rates for GSM Evolution), and UMTS (Universal Mobile Telecommunications System). Various generations of these technologies exist and are deployed in phases, with one common third generation (3G) UMTS-related modality referred to as UMTS-FDD (frequency division duplexing) being W-CDMA (Wideband Code Division Multiplexing). Besides mobile communications modalities such as these, mobile phones also incorporate local area data networking modalities such as Wireless LAN, or WLAN (IEEE 802.11x).
A fundamental component of any wireless communications system is the transceiver, that is, the combined transmitter and receiver circuitry. The transceiver encodes the data to a baseband signal and modules it with an RF carrier signal. Upon receipt, the transceiver down-converts the RF signal, demodulates the baseband signal, and decodes the data represented by the baseband signal. An antenna connected to the transmitter converts the electrical signals to electromagnetic waves, and an antenna connected to the receiver converts the electromagnetic waves back to electrical signals.
Conventional mobile handset transceivers typically do not generate sufficient power or have sufficient sensitivity for reliable communications standing alone. Thus, additional conditioning of the RF signal at both the transmission end and the reception end is necessary. The circuitry between the transceiver and the antenna that provide this functionality is referred to as the front-end module, which includes a power amplifier for increased transmission power, and/or a low noise amplifier for increased reception sensitivity. Depending on the link distance and selected quality of service levels, the RF carrier signal is amplified to the designated level, and delivered to the antenna.
In general, a communications link is established when both the transmission and reception of a signal are in accordance with mutual parameters, with one such parameter in the case of wireless RF communications being the carrier frequency. Emissions outside the established carrier frequency are unnecessary and indeed undesirable, as they have the potential to interfere with other wireless systems. Moreover, there are regulatory requirements that govern the acceptable emission levels of signals outside of the carrier frequency to ensure that different communications devices can co-exist and function properly within the same vicinity. The highest power of unwanted signals at the RF power amplifier is typically generated at the harmonic frequencies of the carrier signal fundamental frequency, which is primarily attributable to the non-linear response of the active devices (e.g., transistors) used for amplification. For example, with a typical RF power amplifier operating in the 2.4-2.5 GHz ISM (Industrial Scientific Medical) band at relatively high power levels of greater than 20 dBm, which is characteristic of WiFi, Bluetooth, and ZigBee wireless communications modalities, the power levels of the harmonic frequency emissions can exceed United States Federal Communications Commission limits of −41.3 dBm by over 40 dB at the third harmonic frequency, and by over 50 dB at the second harmonic frequency.
Conventional RF power amplifiers thus incorporate harmonic filters to minimize the level of undesirable emissions. One possible way to reduce harmonic emissions is by way of a low-pass filter that rejects all frequencies above the fundamental frequency, while another possibility is a notch filter that rejects only certain harmonics as defined by the particular communications standard. In order for the filter to be able to reject high levels of harmonic frequencies, components having low loss such as capacitors and inductors are utilized. However, implementation of harmonics filters in integrated circuits is challenging because of the significant losses associated therewith, particularly as they relate to metal and substrate losses. Furthermore, because of the large footprint of inductors in integrated circuits, the overall cost can be substantially increased.
Accordingly, there is a need in the art for improved on-die harmonics filtering for RF power amplifiers. There is also a need for such harmonics reduction to be implemented without inductors to overcome the aforementioned issues associated therewith and more.